1. Field of the Invention
The present invention relates, in general, to a vehicle steering apparatus and, more particularly, to an energy absorbing, collapsible steering apparatus.
2. Description of the Art
In today's vehicles, steering columns are typically designed to collapse during a collision so as to dissipate energy due to the occupant's impact with the steering wheel. Various steering columns have been devised to collapse when a certain force level is applied to the steering wheel by the occupant. Such steering columns are designed of two telescoping, tubular members. Various elements, such as frangible members, collapsible bellows, bearings, perforated sleeves, etc., are interposed between the overlapping portions of the tubular members to control the rate of collapse and to establish a predetermined force level required for the start of collapse of the steering column.
Recent federal standards requiring passive occupant restraint, which have resulted in the installation of inflatable air bags in the steering wheel, have imposed new requirements on the design of energy absorbing steering columns. Mechanically actuated air bags require that an impact force be transmitted from the bumper, through the frame, steering gear and steering column to an initiating sensor in the steering wheel. Thus, the steering column must remain intact for a certain amount of time prior to the initiation of any collapse in order for the deployment of the air bag to properly occur. The previously devised steering columns, while collapsible, do not sufficiently control the force versus displacement curve of the steering column to permit reliable use with an air bag.
Further, in such a collapsible steering apparatus, the steering shaft itself which is interconnected between the steering gear and the steering wheel must also collapse. Accordingly, such steering shafts have been formed of two separate shaft sections which are telescopingly engaged at one end. Various means have been employed to interconnect the overlapping ends of the two steering shafts to provide for simultaneous rotation of the shafts during normal use of the steering apparatus as well as to prevent any backlash or play between the two shafts. Grooves and through bores have been formed in the overlapping portions of the two shafts and filled with a moldable plastic to secure the shaft sections initially in place. The plastic is sheared by force applied to the steering wheel to enable telescoping collapse of the steering shafts. However, this technique is time consuming and requires additional manufacturing operations which add to the cost of the steering apparatus.
Thus, it would be desirable to provide a collapsible, energy absorbing steering apparatus which provides predictable force versus displacement characteristics during collapse. It would also be desirable to provide a collapsible, energy absorbing steering apparatus in which the collapse resisting force may be varied to any desired amount to meet various application requirements. Finally, it would be desirable to provide a steering apparatus in which the predictable force versus displacement characteristics can be easily implemented in an existing steering column without extensive modification to the steering column.